The instant invention resides in the art of antiskid systems for braked-wheel vehicles. While the system described hereinafter will be with respect to the adaptation of the invention to an antiskid system for an aircraft, it will be understood that the invention is equally applicable to all vehicles having antiskid systems. The invention is particularly related to improvements in antiskid systems and provides a means whereby an operator may make an operational check of the antiskid system at any of a number of times prior to calling upon the system in assisting in the braking of the vehicle.
Heretofore in the art, quite a large number of antiskid systems have been known and utilized. Present day systems are of a rather sophisticated and complex nature, this sophistication and complexity increasing the possibility of system malfunction. State-of-the-art antiskid systems include AC/DC converter circuitry connected to a transducer and supplying a voltage to a deceleration or rate detector. A skid detector is often controlled by the deceleration detector and is operative for controlling a modulator which, in turn, controls the reapplication of brake pressure which has been released upon sensing of a skid. Of course, such systems include electrohydraulic valves interconnected with the skid detector, modulator and, often times, locked wheel prevention circuitry. Each of the foregoing subcircuits of an antiskid system performs a vital function in the operation of the system and the control to be achieved thereby. Accordingly, it is desirable that a pilot or other operator be able to ascertain the operativeness of the system prior to its use.
In the past, there has been no extensive test available for testing an antiskid system on board. Indeed, it has been the practice of the aircraft industry to occasionally perform individual tests on the various wheels of an aircraft to determine whether the antiskid system was operative for that wheel. Such tests were not built into the aircraft and so require an extensive amount of work to perform. Hence, such tests were performed at rather spaced intervals on a routine basis. Of course, if the pilot felt that the antiskid system was not working properly, such as by the blowing of a tire on landing, further extensive tests of the antiskid system would be made. In the prior art, however, with only periodic rudimentary tests being made of the antiskid systems, problems with the systems were not detected until such problems were actually experienced when the antiskid system was in use. For example, the pilot might not know that the antiskid system on his aircraft was malfunctioning until he had landed on the runway and was in the midst of braking operations. Such late knowledge may result not only in damage to the vehicle, such as blown tires or the like, but also in bodily injury or discomfort to passengers. Therefore, there is needed a built-in test system incorporated with the antiskid system whereby an operator may make frequent functional checks of the system's operability and be apprised of any problem prior to the time when braking efforts would call upon the system to function. By being forewarned of such problems, the pilot or other operator may simply land more carefully and manually modulate brake pressure to achieve a safe and comfortable landing.